A project of Columbia University, "SEDACs mission is to develop and operate applications that support the integration of socioeconomic and earth science data and to serve as an information gateway between the earth sciences and social sciences." In addition to a host of interactive mapplications, they host a large number of academic data sets on a wide variety of topics.
"The North American Religion Atlas (NARA) provides access to resources for the study and teaching of North American religious history within a geographical and multimedia framework. Using mapping technology, users can view data on religion at national, state or county levels. Text, image, and multimedia formats are also available and contribute to greater understanding of the story of North American religion."
A local New Jersey watershed protection organization sponsors this regional GIS clearinghouse. They've got lots of good content from over the years, most of it focused on the Northeast and environmental data collection/visualization.